The Investigation of Insulation Performance Evaluation of the Large Electrical Rotating Machine in Frequency Domain

The insulation structure of winding in a large electrical rotating machine consists of epoxy resin and mica material. The insulation structure is composed of many junctions. The insulation problems generate different kinds of signals, such as electromagnetic waves, which may get released from the non-perfect characteristics of the enclosure. This signal may interfere with the functioning of other nearby electronic devices. Therefore, maintaining an excellent condition of the insulation system of the machine is very important. For a condition monitoring of this insulation as proposed in this research, it is taken into consideration the results of the polarization and depolarization current (PDC) measurement of the test sample, and the stator winding rated 13.8 kV was investigated. The experiments were conducted under different thermal stresses, i.e., 25°C (the room temperature) and 100°C (the operation temperature). The test samples were divided into three types: I. haft-overhang, II. overhang and III. full stator bar. From the PDC measurement data record, the complex capacitance and polarization losses (ion migration polarization, slow relaxation polarization and interfacial polarization) were calculated. It was found that the aging of the insulation related to the complex capacitance and polarization losses can be contributed for research in future wireless technology.

Permittivity experimental determination as a frequency function

Objective: To determine the behavior of dielectric permittivity of class II ceramic capacitor in function of frequency up to 10MHz. Context: in telecommunications and high frequency circuits is necessary to take into account the diminishing of permittivity on dielectrics of ceramic capacitors with the frequency growth, two quantitative methods are proposed to determine this behavior. Method: First, the impedance meter bridge FLUKE PM5306 was used in the frequency range from 10^2 Hz to 10^5 Hz; and second, a novel low-cost electronic circuit for the frequency range between 10^4 Hz to 10^7. Results: The results from the circuit were validated using the impedance meter bridge RLC FLUKE PM 6306. The measure of the complex capacitance from three capacitors and their loss tangent were obtained. Conclusions: The capacitance decreasing with the increment of the frequency was observed in the impedance meter bridge and the implemented circuit, finding a convergence between both methods in the common frequency region.

Aging Behavior and Electric Field Induced Instabilities in Lead Magnesium Niobate - Titanate Relaxor Ferroelectric Single Crystal

The aging characteristics and influence of electric field poling on the phase transitions in (1-x)Pb (Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) [110]-oriented single crystal were examined through temperature dependent complex capacitance study. In addition to two phase transition anomalies exhibited by the crystal in the virgin state, other phase transition instabilities were observed in the complex capacitance of the crystal under the external applied electric field. The aging behavior deviated from the linear logarithmic law and followed the stretched exponential expression typical for relaxor ferroelectrics. Moreover, aging decreased with frequency while it became faster with increase in temperature towards the paraelectric – ferroelectric structural phase transition temperature.

Fabrication and Electrical Properties of Strontium Doped Lanthanum Manganite Titanite Oxide

Composition of La0.7Sr0.3Mn0.4Ti0.6O3has been prepared using solid state reaction method where its crystal structure and electrical properties has been analyzed using X-ray Diffractometer (XRD) and Low frequency LCR meter, respectively. The result, shows that the sample has cubic perovskite structure with the existence of impurities phase. In electrical measurement, the frequency dependence of complex capacitance plot shows the sample have strong dispersion at lower frequency and the impedance plane plot shows a semicircle due to the grain effect. The sample electrical properties are also represented in equivalent electrical circuit which consists of a quasi d.c and in parallel with conductance.